As it turns out, this pattern has some major issues: The right front panel is shorter than the left and back, the sleeves and armholes are not graded for size, and the shaping of the sleeve is different from the armhole shaping.

Had I known about these issues I would NEVER have picked this pattern to be my first sleeve-seaming experience! (Note to self: From now on, read about the projects on Ravelry, don't just look at the pretty pictures!!)

Anyway, I got lucky with the front panels - when I decided to change the number of buttons (see previous thread), by sheer chance I used the row count from the left front to calculate the new buttonhole placement.

Now, the sleeves are finished, and the body is up to the armhole shaping. I have put so much work into it so far, and I think it has the potential to be a nice sweater, but I really don't want to ruin it with wonky and ill fitting sleeves (that are also a pain to seam).

So, what can I do to make the sleeves a bit roomier (add one size), especially in the top, and possible fit the armhole shaping a bit better? I'd still want to go for a gathered look on the shoulder. They're knit top down, so I would have to frog them to make the changes, which I'm ok with.

Are there any changes I should make to the armhole shaping?

From the armhole shaping section and onward, the front comes out six rows longer than the back, is this another mistake in the pattern (wouldn't the back usually be longer)?

Anything else I can do to make it look and fit better (and possibly easier to work with)?

Here are the pattern directions:

Armhole shaping, back:
Continue in the pattern, casting off 3 sts at the beginning of each of the next 6 rows, then work 2 sts tog at the beginning of each of the following 6 rows (68 sts). Work 28 rows without further shaping. Cast off.

Front (left and right), armhole and neck shaping: (50 sts to start)
Cast off 3 sts at the beginning of the next row and every following alt row at armhole edge, 3 times, then work 2 sts together at the armhole edge of every alt row 3 times, when the armhole shaping will be finished. AT THE SAME TIME, slope the neck by working 2 sts tog at the neck edge of every third row until 26 sts remain. Work 10 rows without shaping. Cast off.

Sleeves (worked from top):
Using 4.5 mm needles cast on 26 sts.
Row 1: *K2, P2, repeat from * to end.
Row 2: Inc in the 1st st, P until 1 st remains, inc.
Row 3: Inc, K3, *P2, K2, repeat from * to end, but inc in the last st.
Row 4: As row 2.
Row 5: Inc in the 1st st, *P2, K2, repeat from * until 3 sts remain, P2, inc in the last st.
Repeat from the 2nd row until 80 sts. (at which point I joined in the round)
Continue in pattern for 32 rows more.

You could go up a size for the sleeves or just extend the increases to make the sleeve wider but if you widen the sleeve, you'll need to check that it will fit into the armhole opening. Of course, you can always gather the top of the sleeve cap a bit to ease it into the opening. It might be best to finish the front and back and then join them at the shoulder before re-doing the sleeve. That will give you an idea of the size at the armhole. The fabric is supposed to be quite stretchy according to the Rav notes so perhaps you won't need to increase very much?
I wouldn't worry too much that the shaping isn't exactly the same between sleeve and sweater body. You will seam along the edges even if they don't precisely align.

I would go up a size in the sleeves if there was more than one size, but the pattern only gives directions for one sleeve that is supposed to fit all 5 sizes. The fabric is quite stretchy, but the sleeves loose some of their puffiness as they're stretched. A larger sleeve cap would not be a problem, I don't think, as it's meant to be gathered at the top anyway. I suppose I am really looking for information on how to grade sleeves.

The problem with the difference between the shaping in the armhole and on the sleeves, is that the underside of the sleeve increases by 1 st on each side every row and finishes in a point under the arm, whereas the body has a 6 st bind off edge under the arm, and then decreases in steps of 3 sts on either side every other row. So it's a matter of joining something pointy to something flat, which I am having a very hard time visualizing. (I attached a pic of the underside of the sleeve, fyi one pattern column is 4 sts wide.)

You could increase 2sts on each end in some of the rows (say, increase in the first and last two sts) or you could cast on 3sts on either side of the last two increase rows. That would widen the sleeve and match the front and back bind offs. Another way is add increase rows which will widen the sleeve and also deepen the sleeve cap.
It's a beautiful color which looks wonderful in this pattern stitch.

That sounds really great. I especially like the solution of adding width by casting on 3 sts at each end of the last increase row - if I'm counting right, it should allow me to stay in pattern, as well as taking care of my seaming anxiety. I think I'll finish the body and pin everything together so I can see exactly where the sleeves need the extra help.